1. Field of the Invention
The present invention is directed to an improved kiln car for transporting an increased throughput of product through a kiln and, more particularly, to a kiln car having a refractory superstructure of reduced mass and improved thermal barrier means of low heat capacity to prevent heat damage to the carriage of the kiln car, and to permit more efficient use of energy in the kiln while increasing the product throughput per car per day.
2. Review of the Prior Art
Kiln cars presently employed and/or described in the prior art use a steel carriage adapted to be mounted on a track for rolling the kiln car through a high temperature kiln; for example, a tunnel kiln. Mounted on the carriage are refractory materials sufficiently large and of a high mass and forming a solid base to support the setting refractories or product to be fired, to provide a thermal barrier for the steel carriage, so that the bearings and other moving parts are not affected by the heat. To improve the thermal barrier means, the spaces between the steel "I" beams of the carriage are filled with various insulating materials, such as described in U.S. Pat. No. 1,306,160. In U.S. Pat. No. 1,333,381, a specially designed kiln car is described having a superstructure in which the heated atmosphere circulating in the kiln is brought into direct contact with the product to be fired but also protects the product from the direct impact of the heat being introduced into the kiln. In U.S. Pat. No. 1,587,210, a kiln car for use in a tunnel kiln is described in which the car superstructure includes a specially designed imperforate layer made of a ceramic-bonded silicon carbide or crystalline alumina on which ware to be fired can be placed without the use of saggers. In U.S. Pat. No. 1,694,749, a kiln car is described in which the superstructure is arranged with shelves or trays which may be adjusted to varying heights to suit articles of various heights. In U.S. Pat. No. 1,777,856, a kiln car is described in which a layer of refractory bricks are placed on the steel carriage to provide an insulating barrier. In U.S. Pat. No. 2,879,577, an improved superstructure having horizontally-spaced shelves, supported by pillars, is described. In U.S. Pat. No. 3,377,670, an improved car top tile for kiln trucks is described. In U.S. Pat. No. 3,759,661, a low thermal mass kiln car is described in which nonload-bearing, thermal-insulating material forms part of the refractory superstructure. A plurality of posts for carrying an upper deck to support ware to be fired are mounted on the carriage of the kiln car and project upwardly through the thermal barrier. The posts are supported with lateral stability by sockets formed in the base. In U.S. Pat. No. 3,997,289, a kiln car is described having a refractory superstructure formed of a number of tiers one above the other, each being supported by refractory batts. From the foregoing, the concerns of the prior art included providing kiln car superstructures with sufficient refractory mass to prevent damage to the carriage. Also various attempts to reduce the mass of refractory by using thermal-insulating materials have been made. However, the problem of providing a refractory superstructure having sufficiently reduced heat conductivity to the steel carriage structure remains. Also, present refractory superstructures do not provide for an increase in throughput of product per car per day through a kiln with a resulting reduction of energy per piece fired.